This invention relates to processes for the preparation of polybenzazole fibers and fiber filaments.
Fibers prepared from polybenzoxazole (PBO) and polybenzothiazole (PBT) (hereinafter referred to as PBZ or polybenzazole polymers) may be prepared by first extruding a solution of polybenzazole polymer in a mineral acid (a polymer "dope") through a die or spinneret to prepare a dope filament. The dope filament is then drawn across an air gap, with or without stretching, and then coagulated in a bath comprising water or a mixture of water and a mineral acid. If multiple filaments are extruded simultaneously, they may then be combined into a multifilament fiber during or after the coagulation step. The filament or fiber is then washed in a washing bath to remove most of the mineral acid, and then dried. The physical properties of such filaments and fibers, such as tensile strength, are known to be relatively high. However, further improvement in such properties is desirable.